The long term goal of this project is to determine the metabolic fate of the thyroid hormones and the relationships between hormone metabolism and hormone actions. The project is oriented towards the understanding of human thyroid physiology and thyroid disease, and emphasis will be placed on studies in human subjects. Specific areas of investigation will include: (1) The extrathyroidal conversion of thyroxine (T4) to triiodothyronine (T3), usng new techniques to estimate the rate of conversion, and studying the effect of various drugs and disease states on conversions; (2) The peripheral metabolism of T4 and T3 in pregnant women and the rates of transfer of hormones to the fetus, studying patients who are undergoing therapeutic abortions; (3) Changes in hormone metabolism in infection; (4) Pathways of thyroid hormone metabolism in various tissues in vitro including leukocytes, thyroid, pituitary, liver, and kidney; (5) Effects of cold on T4 and T3 turnover in baboons.